1. Field of the Invention
The present invention relates to dust capture devices using a filter, in particular to a dust capture device having the capability of automatically renewing and cleaning a filter, and a projection type image display apparatus using the dust capture device.
2. Description of Related Art
Projection type image display apparatuses such as a projector include image display elements, such as a liquid crystal panel and a digital mirror device (DMD), and produce large-screen images by concentrating strong light from a light source, such as a lamp, onto the image display elements, and magnifying and projecting optical images formed by modulating the strong light in accordance with input image signals.
The image display elements that are subjected to strong light, the light source itself, the device power supply and the like generate a large amount of heat. Thus, they may be damaged thermally unless they are cooled appropriately. Therefore, projection type image display apparatuses generally utilize a configuration such that the inside thereof is cooled by introducing outside air through an air intake using a fan.
However, dust also may be introduced to the inside together with the outside air. The adhesion of the dust to optical parts, such as the image display elements and prisms, and to parts in the vicinity of the light source causes a reduction in luminance and color unevenness. Hence, a filter for capturing the dust is disposed at the air intake. A urethane filter that is used primarily as such a filter, however, needs to be cleaned every several hundred hours. Further, an electrostatic filter that can collect much smaller dust cannot be cleaned, so that it needs to be replaced with a new filter every several hundred hours.
On the other hand, most of the projection type image display apparatuses are used by being hung on the ceiling, in other words, they are placed at an elevated position. Consequently, since they are not in an installed position where filter renewal can be carried out easily, the filters may not be always in an adequate condition.
The urethane filter prevents the entry of dust by capturing the dust physically with small openings but it cannot prevent the entry of dust smaller than 10 μm. Therefore, the urethane filter cannot prevent the entry of yellow sand or cigarette smoke particles. In contrast, the electrostatic filter can capture small dust because the dust is captured using static electricity, while it has openings that greatly suppress loss of pressure.
In view of the situations as above, JP H5-49830 A, for example, discloses the following structure as a solution to a similar problem.
According to JP H5-49830 A, an electrostatic filter for an ozone deodorizing device is formed in a long belt shape and is stretched between two rotation rollers windably. The electrostatic filter wound around one of the rotation rollers is taken up automatically by the other rotation roller using a driving motor in accordance with the deodorizing operation time.
In this way, by using the take-up type electrostatic filter and taking up the filter in accordance with the operation time, the unused part of the electrostatic filter is moved to a ventilating unit, and thereby the number of filter renewing operations can be reduced.
It appears that by applying the configuration disclosed in JP H5-49830 A to a projector, a time interval between filter renewing operations similarly can be extended. However, even when the electrostatic filter itself is still in a state of having a dust capture capability, the effect of static electricity cannot be achieved when a large amount of dust adheres to the filter. As a result, dust may enter the device without being captured.
Thus, the electrostatic filter needs to be renewed in a brief period of time in a dusty environment unless the size of a space for housing the filter is increased.
However, an increase in the size of the space for housing the filter results in an increase in the size of the projection type image display itself, and furthermore, the usage of the filter increases. These go against the recent trend of space and resource savings.